Death in the Andamans

The enchanting islands in the Indian Ocean beckon irresistibly, though Copper Randal soon discovers that paradise has a darker side, and a sense of foreboding hangs in the hot stillness among the mango trees and coconut palms. But neither she nor her friend Valerie, stepdaughter of the Islands' Chief Commissioner, anticipate the sinister climax to their hurricane-struck picnic.
And when one of their party is presumed drowned and another is mysteriously murdered, Copper and her friends, stormbound and marooned on tiny Ross Island with no links to police or doctor, must turn detective to save their own lives ...

M. M. Kaye